Corresponding cutting bits or inserts and a corresponding milling tool are known for example from U.S. Pat. No. 4,867,616. In the known milling cutter the cutting inserts are approximately of a square basic shape with interrupted cutting edges which are bevelled in the corner regions. The individual plates are distributed in alternate axially slightly displaced relationship along the periphery of a tool body which is cylindrical or in the form of a disk, so that overall two different groups of cutting inserts are arranged in such a way that the one group of cutting inserts projects in the one axial direction and the other group of cutting inserts projects in the other axial direction, beyond the thickness of the disk-shaped tool body. All cutting inserts also project slightly in the radial direction beyond the radius of the main tool body and they are received in corresponding recesses or receiving pockets in the main body of the tool. In that arrangement the active cutting edges are not oriented exactly parallel to the axis of the tool body but are slightly inclined relative to the axis, that is to say they are slightly tilted in a plane which is defined by the associated radius vector and the axis of the tool body.
The displacement of the two cutting insert groups relative to each other provides that the cutting edge portions of the one group of cutting inserts cut substantially in the gaps of interruptions formed by the interrupted cutting edges of the other group of cutting inserts. That provides that, even when both groups of cutting inserts overlap to a relatively great extent in the axial direction, the cutting inserts are nonetheless substantially uniformly loaded along their entire (even if interrupted) cutting edges.
The cutting inserts can be turned and have up to eight (interrupted) cutting edges. Corresponding milling cutters can be used to cut for example slots or grooves in workpieces. A corresponding milling cutter is only limitedly suitable for the production of camshafts and at any event would require a plurality of successive working operations in order to produce the correct cam profile.
In the recent past the quality of the cutting inserts or the material from which they are produced has increasingly improved so that accordingly it has also become possible to use further increasing machining speeds without the risk of the cutting inserts being damaged or suffering from excessively rapid wear. It will be noted however that these higher machining speeds also entail the disadvantage of an increased production of noise. In the case of almost all milling cutters and almost all milling operations, the cutting edges or at least a part of the cutting edges are or is not permanently in engagement with the workpiece which is in the course of being machined, but on the contrary the cutting edges come into engagement and out of engagement again with the workpiece intermittently, the engagement position extending only over a given angular region of the corresponding rotating milling tool. After a rotary movement through a given angle, depending on the nature of the machining operation and the depth of engagement, the previously active cutting edges of a cutting bit initially come out of engagement with the workpiece until, after a rotary movement through a further angle which in total generally affords an angle of 360.degree. with the first-mentioned angle, they come into engagement with the workpiece again, and the corresponding process begins afresh. That applies in regard to each individual cutting insert arranged along the periphery of a corresponding milling cutter, in which case during a workpiece machining operation a respective part of the cutting inserts which are distributed over the periphery are in engagement with the workpiece while another part is just out of engagement therewith.
Engagement of an active cutting edge with the workpiece is generally effected abruptly after a corresponding rotary movement of the tool body, insofar as the respectively active cutting edge which is substantially parallel to the axis comes into engagement over its entire length simultaneously with the workpiece and a chip or a plurality of chips are detached from the workpiece material during the further rotary movement in the workpiece material. The moment of coming into engagement, by virtue of the cutting edges striking against the workpiece or the surface to be machined, causes a noticeably audible noise and the large number of cutting edges of the individual cutting inserts, which come into engagement with the workpiece surface in rapid succession during a rotation of a milling cutter, produce a considerable amount of noise in the case of a milling cutter which is rotating fast.
In that respect industrial health and safety requirements provide that a noise level of 80 decibels is not to be exceeded by corresponding tools, in which respect the noise level is measured at precisely defined distances relative to the workpiece and the milling cutter. With an increasing machining speed, that is to say with an increasing speed of rotation of the tool bodies or with an increase in the diameter of the rotating tool bodies, the noise level produced further increases. In addition the relevant authorities in Europe are endeavouring to further reduce the maximum allowable noise level of 80 decibels to 75 decibels. This means that the machining speed and therewith also the productivity of corresponding machines would have to be reduced below the value which would otherwise be technically possible.